In order to effectively re-utilize municipal waste, the usual procedure is to segregate the waste so as to recover the re-usable constituents. The rest of the waste is, then, heat-decomposed to generate fuel gas or to obtain liquid fraction and/or is incinerated to utilize heat energy derived thereby. Separation of usable constituents out of waste generally depends on the physical characteristics of the constituents, e.g. magnetism, electrical conductivity, specific gravity, inertia, elasticity, size or the like. Usually, to facilitate the segregating operation, it is deemed necessary to pre-treat the waste by a pulverizer to segregate it to a mono-constituent, respectively and to make the particle size of the pulverized waste uniform.
However, when it is picked up, municipal waste is generally of various kinds, e.g. garbage (food waste such as kitchen refuse), waste paper, scrap wood, waste fibrous material, scrap plastic, glass, and metal and the like. Thus, physical properties of municipal waste are not constant and vary from time to time and from place to place. Therefore it is difficult to reduce such municipal waste into uniform particles by using a conventional pulverizer. Thus, there has been a need for a new and more powerful pulverizer capable of forcibly and uniformly pulverizing the municipal waste by simultaneously applying compression, beat, and shearing. Such a powerful pulverizer has been made, but is unsatisfactory in the points that it is difficult to effectively reduce the waste into uniform particles, it is accomplished by great loss of power and quick wear in the components of the pulverizer, it requires a large amount of electric energy, and maintenance costs are high.
In order to eliminate the disadvantages mentioned above, a pulverizer of a cylindrical rotating cylinder type has been proposed such as for example as disclosed in the cross referenced U.S. Pat. application Nos. 464,219 and 497,275.
These pulverizers proposed in the above co-pending applications work well and effectively pulverize and segregate the municipal waste. However, due to the increase in the amount of the municipal waste to be processed as well as the increasing economical and social demands for recovering useful materials out of the municipal waste, even more efficient pulverization is expected with less loss of power and less maintenance cost.